As a nuclear medicine imaging apparatus, Positron Emission computed Tomography (PET) apparatuses are conventionally known. To perform an image taking process using a PET apparatus, an examined subject is dosed with a compound or a radiopharmaceutical labeled with a positron emitting nuclide. The compound or the radiopharmaceutical with which the examined subject was dosed travels within the examined subject's body, and the positron emitting nuclide is taken into a body tissue of the examined subject. The positron emitting nuclide releases positrons, so that the released positrons are coupled with electrons and annihilated. At this time, the positrons release a pair of annihilation radiation rays (which may also be referred to as “gamma rays” or “annihilation gamma rays”) in substantially opposite directions. The PET apparatus detects the annihilation radiation rays by using a detector arranged in a ring formation so as to surround the examined subject and generates coincidence counting information (hereinafter, a “coincidence list”) from the detection result. Further, the PET apparatus performs a reconstructing process through a back-projection process by using the generated coincidence list and generates a PET image.
Incidentally, during the process of generating the coincidence list from the detection result, the PET apparatus generates data (hereinafter, “event data”) based on an output signal from the detector and transfers the generated event data to a subsequent processing stage. Because this transfer process and the processing at the subsequent stage are subject to hardware restrictions, the PET apparatus usually includes a buffer for storing the event data therein so as to regulate the amount of the event data to be transferred. However, during a high count rate period in which a large number of annihilation radiation rays are detected in a unit time period, the PET apparatus may not be able to regulate the amount of the event data appropriately.